Much of a computer system's functionality and usefulness to a user is derived from the functionality of the peripheral devices. For example, the speed and responsiveness of the hard disk drive is a major factor in determining a computer system's overall performance. Or, for example, the speed with which audio or video files can be retrieved from a DVD-ROM determines the computer system's usefulness as an entertainment device. Hence, the rate at which data can be transferred among the various peripheral devices often determines whether the computer system is suited for a particular purpose. To this end, the electronics industry has, over time, developed several different high-performance peripheral interfaces. One standard interface, the Small Computer Systems Interface (SCSI), has become widely used for connecting external peripheral devices to the host computers.
The SCSI interface is widely used in personal computers and workstations, and particularly in large external peripheral devices such as CD-ROM jukeboxes. CD-ROM jukeboxes are essentially large capacity CD-ROM changers that store a large number of audio CDs or CD-ROMs. A typical SCSI CD-ROM jukebox, such as the SONY-CDL1100 jukebox, has the capability of storing and playing fifty to a hundred audio CDs or CD-ROMs.
FIG. 1 illustrates a block diagram of a conventional SCSI CD-ROM jukebox 100. As illustrated, SCSI CD-ROM jukebox 100 includes two identical SCSI CD-ROM drives 130a and 130b coupled to a host computer (not shown) via a SCSI bus 110. In addition, SCSI CD-ROM jukebox 100 includes a SCSI jukebox controller 140 coupled to receive jukebox commands from the host computer via SCSI bus 110. Further, SCSI jukebox controller 140 is coupled to control robotics mechanisms (not shown) for mechanically moving CD-ROMs into and out of SCSI CD-ROM drives 130a and 130b. SCSI jukebox controller 140 is coupled to provide "load/unload" signals to SCSI CD-ROM drives 130a and 130b for controlling the of loading and unloading of the CD-ROMs. SCSI jukebox controller 140 may also be coupled to SCSI CD-ROM drives 130a and 130b to receive status signals such as chucking and unchucking status of the media. A front panel interface 150 having a LCD screen 152 for displaying status and error message of the SCSI jukebox controller 140 may also be coupled to SCSI jukebox controller 140. Further, as illustrated, SCSI CD-ROM drives 130a and 130b, and SCSI jukebox controller 140 each includes SCSI LSI circuits 141, SCSI firmware 142, and embedded processor 143 for processing SCSI commands.
In operation, SCSI jukebox 100 receives jukebox command signals from the host computer (not shown) via SCSI bus 110. According to the jukebox command signals, the SCSI jukebox controller 140 sends control signals to the robotics mechanism for controlling the movement of the CDs or CD-ROMs. SCSI jukebox controller 140 also sends "load/unload" signals to the SCSI CD-ROM drives 130a and 130b for controlling the timing of the loading and unloading of the disks and chucking and unchucking of the media. SCSI jukebox controller 140, however, does not control access operations, such as playing and pausing, of the SCSI CD-ROM drives 130a and 130b. Rather, the host computer accesses the SCSI CD-ROM drives 130a and 130b using SCSI CD-ROM driver software resident in the host computer. In some conventional SCSI jukeboxes, a user can also control the loading and unloading of the SCSI CD-ROM drives via control knobs 151 of front panel interface 150.
Although conventional SCSI CD-ROM jukeboxes (as shown in FIG. 1) are useful for their intended purposes, one significant drawback of such SCSI CD-ROM jukeboxes is that only two such jukeboxes can be daisy-chained together in one system. The SCSI interface allows only eight devices (e.g. eight IDs) to be coupled to the SCSI bus, whereas each jukebox unit 100 includes at least three SCSI IDs--two IDs for the SCSI CD-ROM drives, and one ID for the SCSI jukebox controller. In today's computer applications, particularly in database systems where literally thousands of CD-ROMs are used, the limitation in the number of daisy-chainable jukeboxes significantly undercuts the usefulness of these devices.
Another significant drawback of conventional SCSI CD-ROM jukeboxes 100 is that the manufacturing costs are high. SCSI CD-ROM drives included in SCSI jukeboxes 100 are quickly becoming extinct in a market dominated by AT Attachment Peripheral Interface (ATAPI) CD-ROM drives. Most CD-ROM drive makers have abandoned the SCSI market due to an eroding profit margin and low volume. This is especially true for the DVD-ROM drive market where high-speed SCSI DVD-ROM drives are virtually non-existent. Thus, it is not cost effective to manufacture CD-ROM or DVD-ROM jukeboxes using SCSI devices.
In addition, a high developmental cost for SCSI jukeboxes makes these devices even less cost-effective. The SCSI interface is complicated and requires expensive SCSI LSI circuits and firmware. Ironically, using the SCSI interface in the jukebox is not particularly advantageous. For instance, most parts of the complicated SCSI LSI circuits and firmware are unused because only simple commands, such as "move" or "check status," are sent infrequently from the host computer to the SCSI jukebox controller 140. Furthermore, communication speed between the host computer and the SCSI jukebox controller 140 can be slow because it takes seconds or tens of seconds for the robotics mechanism to move and retrieve the CD-ROMs.
Furthermore, in conventional SCSI CD-ROM jukeboxes, the SCSI jukebox controller 140 only controls the timing of loading and unloading of the CD-ROMs. No other communication paths exist between the SCSI CD-ROM drives and the SCSI jukebox controller. Thus, inventory information is not shared between the CD-ROM drives and the jukebox controller 140. Although it is technically possible to include a data path between the SCSI CD-ROM and the SCSI jukebox controller such that inventory information may pass from the drives to the jukebox controller, that solution requires an additional set of SCSI firmware, and further increases the costs for such CD-ROM jukeboxes.
Thus, what is needed is novel jukebox for computer-readable media which overcomes the aforementioned shortcomings of conventional SCSI CD-ROM jukeboxes. The present invention provides a novel and unique solution that is cost-effective and can be easily built from existing components with minimal modifications.